Vegetation Layers in an English Woodland

The different layers within a woodland are one of those classic illustrations from ecology textbooks – usually a cartoon graphic showing how the structure changes as you move from the ground up to the canopy. The distinctions are indicative – there is often plenty of overlap between the layers – but these are a useful way of thinking about the woodland in terms of its ecological function beyond what simply meets the eye. Helping you to see the wood for the trees, if you will!

We undertake tree climb and inspect surveys for bats in a variety of settings – from individual trees in gardens to well-spaced parklands and dense woodlands. Each of these gives a different insight into vertical variation but a recent climb in an oak and ash woodland gave a nice opportunity to illustrate how this changes in a typical ancient woodland habitat.

English Oak Woodland Structure
Photographs taken at 2m (bottom), 6m (middle) and 12m (top) in an English oak and ash woodland to illustrate the variation in spatial structure.

The number of ‘layers’ and their distinctions vary between sources and across countries – I’ve seen three defined layers, nine defined layers and every number in between delineated in various graphics. I’m going to keep this simple and focus on the three broad categories which are shown in these photos:

Field Layer – taken at 2m height

Ground Layer
Photograph taken at 2m showing the field or ground layer in an English oak and ash woodland

 

This photograph encapsulates what could be considered the field layer, the ground layer or the forest floor depending on which divisions you use. Broadly, this is the view from the ground – the most apparent vista for most visitors to the woodlands but the scene varies greatly as the year progresses. In secondary woodland or more botanically diminished sites, this can be a mass of ruderals such as nettles, cow parsley and bramble whilst some plantation woodlands can be head-high in bracken. In ancient woodland – such as this – springtime sees a flush of ancient woodland species which time their flowering early in the season before the canopy closes overhead. As May arrives and the trees and shrubs come into leaf, the main event on the forest floor is already coming to an end. Some species flourish later in the season but in September, the vegetation has largely died back often leaving a relatively bare floor. The dominant vegetation remaining is therefore the trunks of the trees and the shrubs which rise above the field layer to leaf and flower higher.

Scrub Layer – taken at 6m height

Shrub Layer
Photograph taken at 6m showing the hazel-dominated shrub layer in an English oak and ash woodland

This could be described as the under-canopy, the scrub layer, the shrub layer or the under-storey layer. This is the level at which the shrubs flourish – those smaller woody species which often include hawthorn, blackthorn, hazel, holly, dogwood and elder, amongst others. These shrubs can often form such a dense canopy that the view to the treetops above can be quite obscured – something of an issue when you’re searching for bat roosts! In this instance, hazel and hawthorn dominate and as the photograph shows, they form a dense and highly cluttered environment some 6m above the ground.

Canopy Layer – taken at 12m height

Canopy Layer
Photograph taken at 12m showing the space between the shrub layer and the woodland canopy in an English oak and ash woodland

This is up at the top of the trees, where the taller trees branch and close their canopies to claim first use of the sunlight available. I’m not right in the canopy in this photograph – the trees did not require us to climb to the peaks – but this nicely illustrates the shrub layer below with the high canopy of the oak and ash above. In some forests, the species composition includes a sub-canopy of smaller trees – such as rowan, silver birch and field maple – which form a layer between the lower shrubs and the taller climax species. This photograph nicely illustrates how much of a space can open up between distinct layers within the higher reaches of the forest structure.

Why does it matter?

An appreciation of how the character and conditions of a woodland change on a vertical plane are just as important, although a little harder to appreciate, than the variation on the ground. The illustrations above are for just one section of just one woodland and each type of species composition but they help to give a visual idea of how this works.

One example of how this type of variation is important is when considering how bats might use a habitat. Different species of bat have different hunting characteristics and habitat preferences, and this often relates to how open or cluttered a habitat is. Species such as brown long-eared are highly maneuverable and will glean insects from leaves so a reasonably cluttered woodland environment suits them perfectly. At the other end of the spectrum, a noctule hawks in open space, often flying over fields and catching its prey on the wing. Species such as pipistrelle are typically characterised as edge specialists which forage along woodland edges, hedgerows and other similar environments.

Pipistrelle
Pipistrelle bats are typically described as ‘edge’ species which forage along the edges of vertical features, such as a woodland edge

The field layer of the woodland looks ideal for a species such as brown long-eared but you might think that it would be too cluttered and enclosed for other species. However an insight into the structure above the shrub layer reveals a mosaic of open space and leaf cover which provides perfect ‘edge’ habitat for a hunting pipistrelle, and the voids between the trees would be perfectly navigable for a noctule in search of a roost. This was the subject of a talk by Ian Davidson-Watts at a recent BCT Bats and Woodland conference which you can read more about in this blog post here.

If you’re looking for tree climb and inspect surveys for bats, do check out this page for further details!

 

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The Grantham Oak

The Oak of Belton Lane – referred to in some places as the Grantham Oak – is perhaps the most surprising and impressive tree in town. The oak stands on the eastern side of Belton Lane, to the north of the town of Grantham, beside a pedestrian crossing and surrounded by a crescent of residential housing. This is not the typical location for a tree which is likely to be over 500 years old!

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The Grantham Oak, dominating the scene with the pedestrian crossing across Belton Lane to one side, and residential housing to the other

The Grantham Oak – a pedunculate or English Oak (Quercus robur) – has a girth of 7.02m when measured at 1.5m above the ground. To give a rough visualisation of this – it would take over four adults reaching finger-tip to finger-tip to hug this tree. Using this measurement of girth, we can estimate the age of this tree – although this is not an exact science, and is subject to speculation over the early growing conditions of the tree and the stresses or privileges it might have endured or enjoyed over the years.Using the methodology produced by John White – the tree may be 530 – 560 years old, indicating a possible planting date around the 1450’s. To put this in context – this is around the time of the War of the Roses; the founding on the Inca dynasty; and when Joan of Arc was burnt at the stake.

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Sunday morning walkers passing the Grantham Oak

The tree is a pollard – this means that in the distant past, it was cut above the height at which animals can graze. This was generally done to faciliate sustainable harvest of a tree either to provide fodder for animals or for wood timber. Retaining the base of the tree but continually taking new growth allows it to be harvested regularly without killing the tree. Indeed, one result of pollarding trees is that they often live for much longer than non-pollarded specimens.

A ‘wolf tree‘ is one which is older and larger than those around it – it often has a shape and structure which seems unaffected by external influences such as shading or competition, whilst it’s establishment means the younger trees grow and develop in response to it. I often see this in woodlands – especially where an old oak is situated towards the edge of a more recent forestry plantation – but the Grantham Oak is an example of a ‘wolf tree’ in a residential setting – the houses which line Belton Road were built to arch in a crescent surrounding this magnificent tree at its centre. This tree is still valued by many who live close or drive past it – it was nominated in the hunt for the UK’s 2014 Tree of the Year competition.

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The Grantham Oak with the crescent of houses set back from the canopy

The map below illustrates the current location of the tree – set at the edge of residential development, a little way offset from the green corridor along the River Witham which passes through the town to the west.

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The OS map below shows the current location of the tree in a changed environment – extensive residential development now covers its previously countryside landscape.

The housing around this tree was only established in the 20th century and inspection of older maps before this date indicate that in 1905, the land around Belton Lane was agricultural countryside.

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This map from 1905 positions the tree opposite entrance road to Harrowby Mill. Beyond the Oak would have been open fields to the east and west in sharp comparison to the residential housing which populates this site now.

The Harrowby Mill, still present but converted to residential use, lies opposite this tree on the west of Belton Lane and this can be seen as the only marked development in close proximity to the tree back in 1835. Although this was almost 200 years ago, even then the Grantham Oak would have been an impressive specimen of some 300 years old and would have stood dominantly across the road as workers left the mill.

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An extract of a map from 1835 showing the approximate location of the tree with the red dot. The road on which the tree is situated – now Belton Lane – was already in existence along with the Harrowby Mill adjacent to it.

This is registered as Tree 2560 on the Woodland Trust Ancient Tree Register – a link to the tree’s individual page can be found here. The tree is included in the ‘40 Special Trees of Lincolnshire40 Special Trees of Lincolnshire‘ book produced by the Lincolnshire Tree Awareness Group (TAG) under the title ‘The Grantham Oak’. The text describing this tree states that it was originally enclosed by Belton Hall Park although a contact at Belton said that the land at Belton Lane was never within parkland indicating it may never have been a ‘parkland’ tree.

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The incongruous yet magnificent Grantham Oak

I have done my best to piece together a little history and information on this tree, but I would love for this to be just the beginning. If you have any information, photographs or stories relating to this tree, please get in touch with me or leave a comment below and I can update the post to grow the story around this magnificent resident of Grantham.

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The Grantham Oak in November 2016 – just beginning to take on the tones of Autumn

For a similar post on one of Grantham’s impressive trees, take a look at this post on the copper beech on the high street!

2016 in trees

Looking back through the photographs I’ve taken in 2016, it’s striking how many trees there are! As with the small things such as wildflower ‘weeds’, it’s easy to take for granted these enormous beings which grow amongst us. The sheer scale of a mature oak or beech is far beyond our magnitude of experience, as is the timescale they can span which numbers many of our lifetimes combined.

Here are just a few of my favourite encounters from 2016.

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These snow-lined branches were in the mountains above Freiburg at the beginning of the year – we took the cablecar from the grey countryside below up into a winter wonderland of freshly fallen snow. I liked the way that the snow outlines the curved architecture of the branches.
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Part of my job involes climbing trees to inspect them for roosting bat potential. On my way up this field-edge tree, the sun came out and I couldn’t resist a quick shadow-selfie!
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This photograph was taken for the Woodland Trust – this is one of the Verdun Oaks which grew from acorns brought back from Verdun after the First World War and planted in towns and cities as a commemoration to the fallen. In the background is Lichfield Cathedral. The Woodland Trust are tracing these trees as part of the commemoration of the First World War – you can read more about these pieces of living history on their website here.
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I spotted this tree sillouetted against the sunrise on a drive across to Norfolk one morning and had to stop off to get a photograph. The tree was in the middle of a field which was not publically accessible, so I only have the shape to go off but this looks like a poplar tree to me – perhaps a black poplar?
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This is the view up to the canopy at Treswell Wood in North Nottinghamshire. This is a Notts Wildlife Trust site which has a precominantly ash canopy. Unfortunately, Ash Dieback was confirmed in one corner of the woodland and targetted trees were felled in an effort to stop the disease spreading. Ash trees are a characteristic part of the British Countryside and one of the most common species in our landscape – it would be a tragedy if they were to go the way of the English Elm.
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I love being out in the countryside at night – we spent much of the summer watching trees to survey for emerging bats so this scene feels very familiar to me. I took a walk out past this tree near Harlaxton one night when the skies were very clear to capture a starlapse with the North Star centred above the dead crown of this oak.
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This is a slightly boosted photograph in terms of colour saturation, but is otherwise untouched. This was a starlapse of a meadow oak but the quirks of lighting led to this rather psycadelic image. The tree and the hillside to the left were occasionally lit by car headlights from the road behind me, and the background cloud was illuminated by the light pollution of Nottingham in the distance. Not your typical tree image but I rather liked the effect!
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These beautiful old beech trees line a trackway which forms part of the Laurie Lee Wildlife Way in Slad. I love trackways which are overarched by tree canopies, and I especially like the idea that Laurie would have walked these tracks. The book Cider with Rosie is a favourite of mine, especially the descriptions of the Gloucestershire vally in which he grew up, so there is a real feeling of walking somewhere familiar, even when exploring this landscape for the first time.
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This is a photograph taken in Wyndham Park in Grantham. The autumn leaves of a beech provide a frame for the Hand and Apple sculpture which commemorates Isaac Newton’s connection with the town of Grantham – he went to school at King’s Grammar which is just beside Wyndham Park, and lived at Woolesthorpe Manor just down the A1 from the town, where the famous apple tree can still be seen today.
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These two majestic field trees stood like sentries on either side of the gateway. This was on a walk in Somerset which explored an ancient landscape full of both recent history – including an old lead working now rewilded as a nature reserve – and ancient history including a number of monuments, burial mounds and barrows.
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This photograph was taken on a farm track footpath which leads to Muston Meadows, an old haymeadow now designated as an NNR. I wanted to try to capture the essence of mid-December in the Midlands – to me that is muddy walks, early sunsets and skeletal trees.
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This photograph was one of several I took of bark patterns in a veteran oak we were climbing to look for potential evidence of bats. This deadwood can be very stable, remaining as a component of the tree for decades after the wood has died, and the patterns etched into the wood represent to the various conditions and experiences which the tree has gone through.
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This photograph neatly finishes where this summary started – back in the mountains above Freiburg. This was taken just before Christmas where we had the magical opportunity to rise up above the clouds and see the sun setting. The fog and cloud was rolling up the valleys, obscuring and revealing treelines, and the sunset coloured the fog in pinks and oranges.

A November Walk in the Quantocks

Sometimes surveys take me further from home, and a Monday morning survey in Somerset invited an early start to take advantage of the opportunity to explore somewhere new. A chance leaf through the Guardian Travel’s Best Autumn Walks section on Sunday night obliged me with an excellent suggestion – a walk from Adscombe across the Quantock hills to Crowcombe and back.

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The drive on the approach to Crowcombe presented this autumnal treat – it’s difficult to get over how beautiful beech trees look in their yellows and golds. The beech is generally considered native only towards the south of Englan, and whilst there are plenty of specimens tp be seen around the Midlands, it’s only really on a trip south that you can really enjoy their autumn exhuberance en masse.

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There must be a name for when something inanimate catches your eye and morphs into something alien. When I was on a field site at uni, I remember we watched a hare stock-still in the woods for a good 5 minutes before realising it was an apt arrangement of log and stick. This piece of branch and moss caught through the wire fence at the beginning of the walk put me in mind of a tiny maurauder breaking through the defences, strangely sinister!

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The walk took me up through Great Wood, managed by the Forestry Commission. The woodland is varied – from dull conifer plantation to glorious semi-natural oak woodland, all punctuated by beech boundaries where the roots pour over the tops of the banks as the trees cling to their precarious looking anchor points. This smartly-spaced plantation of conifers caught my eye, especially the way the light increases as the beech re-asserts itself on the banks which rise up behind.

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There were plenty of mushrooms and fungi to be seen in the woods – this was a particuarly impressive ring around a conifer. I’m not sure on the species but would welcome enlightenment!

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The route I took went close to Dead Woman’s Ditch, and passed through this spectacuarly gnarled sessile oak woodland. These trees are of a considerable age, but the poor quality of the soils and the exposure results in them being relativly small and encourages these gnarled, twisted growth forms. These are ancient woodland sites, many of which had uses for charcoal and tanning in the past. These days, they provide excellent roosts for a range of bat species including rare barbastelle and Bechstein bats.

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The walk back up from Adescombe took me up Quantock Combe – this is the name given to a steep narrow vally which cuts down the hillsides. The stream running through this combe was gentle and shallow, crossable at almost all points, and overshadowed by ferns and bracken.

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Back up to the top once more, I crossed a cow-grazed pasture to reach the Drove Road which took me back towards Crowcombe. This beech-lined trackway has the gnarled roots replacing the rocks in the walls in places, and provides a sheltered passage across the open fields. Sadly, the exposure meant most of the autumn leaves had already been consigned to the wind, but it must be glorious in its peak. This track is probably pre-historic and was once an important trading route. The sunken track bears testimony to centuries of footfalls, which is a truly humbling thought.

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Before the descent back into Crowcombe, I walked up to Beacon Hill to take in the view from the trig point. Here, the scenery changes from the lushious woodlands to a blasted heath with gorse, heather and Deschampsia with the flar agricultural plains stretching out below.

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Despite being well into the middle of November, there were plenty of flowers to be seen along the route including red campion, bramble, gorse, dandelion, herb robert, wood sage, hedge woundwort and heather.

There are many tracks between Crowcombe and Adscombe, meaning there is no need to retrace your steps on a circular walk between the two. The route I took was a pleasant 8 1/2 miles with some good ascents and descents (certainly compared with my neck of the Midlands!). Allow a few hours to meander and explore, there’s plenty to distract you along the way!

Winter Buds ID Part 1 – Londonthorpe Woods

Tree identification in the winter isn’t so difficult as you might think! Broadleaf trees lose their leaves in the autumn and develop buds which remain throughout the winter and these make it very easy to work out which species is which. The Woodland Trust have produced a very handy guide to some of the most common species which shows photographs side-by-side for comparison. If you want to identify them in a little more detail, this little booklet is invaluable and provides a few more diagnostic characteristics such as the architecture and bark types. It even has a handy key which takes you step by step towards the correct identification!

Of course, one drawback of relying on the buds to identify the tree is getting to the buds in the first place, which can be a long way off the ground depending upon the tree in question. So Londonthorpe Woods seemed like an ideal place to begin.

Londonthorpe Woods is located just off Londonthorpe Lane as you leave Grantham to the north-east. The wood was created by the Woodland Trust who planted thousands of trees on the 56ha arable site between 1993-1995. The Woodland Trust continue to own and manage the site.

As the site is so large, I concentrated on the first area you arrive at if you step through the gate from the car park. This area has been planted with a number of our native species which will one day develop into a woodland much more natural in character than it may appear at present. Alder (Alnus glutinosa) and willow (Salix spp.) will grow quickly but remain smaller, as will the silver birch (Betula pendula) and cherry (Prunus spp.). The English oak (Quercus robur) on the other hand will grow slowly and steadily to rise to prominance above the canopy one day, with ash (Fraxinus excelsior) close behind. Finally there are hazel (Corylus avellana), hawthorn (Crataegus monogyna) and blackthorn (Prunus spinosa) shrubs which will form an understorey, along with dog rose (Rosa canina).

Map of the plantation behind the main carpark of Londonthorpe Woods (courtesy of Google Maps).

Each of the species is described briefly below, along with a photograph of the buds to show you what to look for! Click on any of the photos for a larger image.


Alder

Alder buds are red and vaguely conical and remain quite close (appressed) to the stem. They are alternate – each bud is present as an individual rather than a pair and they alternate as you look along the twig, one to the left, then one to the right.

Alder is one of the more helpful tree species in that it often provides extra clues in the winter – the cones are generally present right through until spring time.


Willow

Willow’s are a variable bunch and as well as having several species native to the UK, they hybridise so there is even greater variety than you might expect. I think that this example might be goat willow (Salix caprea) – it will be easy to check when the buds break – goat willow produce fantastic flowers so watch this space! The buds are alternate again, lime green with redness towards the tip.

The presence of both the willow and the alder in this plantation suggests that the ground may be damp – both species are most commonly found along river banks or in other damp conditions. Like the hazel (see below for more details), the willows have been coppiced in this site.


Silver birch

Now this is a species which few will need the buds to identify – the distinct silver banded bark is visible behind the buds in this photograph!

The buds themselves are alternate and on small stems which protrude from the main twig.

Silver birch grow quickly but are relatively short lived – they are often one of the first pioneer species in a new woodland but soon become out-competed by larger, taller trees.


Cherry

Cherry is another difficult species as there are so many ornamental and hybrid varieties to choose from. The buds are alternate and dark brown with scales visible. Cherry is another species where the bark is very useful in the winter – the lines which look almost like horizontal cracks in their shiny bark are called lenticels and these are quite characteristic of cherries.

Although it is difficult to be sure of the exact species, it is likely that the Woodland Trust would have planted one of the native varieties – wild or bird cherry. Of the two, this one looks more like wild cherry (Prunus avium). Again, we can return to check this in the spring or summer!


English oak

The oak has tight clusters of buds especially at the tips. The buds are brown and have lots of scales.

One day this tree will probably tower above the others – think of the Major Oak in Sherwood Forest. For an example closer to home, there is a beautiful mature oak specimen along Belton Lane which you will probably pass on your way to Londonthorpe Woods – more on this magnificent tree in a later post!


Ash

The ash has one of the most distinctive buds – they form jet black pointed cones which really can’t be confused with much else. If you find buds of a similar shape but a different colour, such as grey, think of one of the other ashes which we sometimes encounter such as manna ash.


Hazel

Hazel buds are a greenish red in colour – a little like a red and green apple. They are alternate along the twig which itself is often hairy. Hazel provides a few extra clues in the winter time – the catkins (the male flowers) are often visible and if you look very carefully, you can see the tiny red female flowers on the same branch.

Another clue, depending on the management, is the growth form of hazel. It is often coppiced – that is cut down to the ground – and from here it sends up lots of new shoots which are often allowed to grow for several years before being cut back. The hazels in this plantation have been coppiced.


Hawthorn

The spiky shrubby hawthorn bush is fairly distinctive, even in the winter time. The spikes are generally quite visible and the buds compete with these along the twig. The buds are alternate and a similar dark reddish colour to the twigs.


Blackthorn

Blackthorn buds, by contrast with the hawthorn, are tiny little red dots which appear along the stem. The twigs are often long spikes and the buds appear along these. The colour of the bark of blackthorn is, as you might imagine quite dark, a blackish grey perhaps.


Dog Rose

Another species which you are unlikely to confuse with many others. Native roses grow lower to the ground than the other species in this plantation but can develop quite a shrubby form. The curved rose thorns, like a hawk’s talon, are quite distinctive and the rose hips, still present in January, are another key clue. The buds themselves are a slightly lurid red and grow  alternately up the twig, alongside the thorns.